May, 1953 
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3URKS: THE Mayr ties oF ILLINOIS 115 
ures 
256 
& 258 
263 
107 
265 
Fig. 255.—Baetis intercalaris, head of adult male, dorsal aspect. 
Fig. 256.—Baetis flavistriga, head of adult male, dorsal aspect. 
Fig. 257.—Callibaetis fluctuans, head of adult male, anterior aspect. 
Fig. 258.—Baetis intercalaris, labial palp of mature nymph. 
Fig. 259.—Baetis brunneicolor, \abial palp of mature nymph. 
Fig. 260.—Callibaetis skokianus, male genitalia. 
Fig. 261—Heterocloeon curiosum, labial palp of mature nymph. (After Ide.) 
Fig. 262.—Baetis vagans, labial palp of mature nymph. 
Fig. 263.—Baetis frondalis, labial palp of mature nymph. (After Ide.) 
Fig. 264.—Callibaetis fluctuans, claw of middle leg of mature male nymph. 
Fig. 265.—Callibaetis ferrugineus, claw of middle leg of mature male nymph. 
crossveins form two or more quite irregular 
: rows across the wing, fig. 222. The hind 
wing is well developed, with abundant cross- 
veins. 
The bodies in most species of this genus 
| are thickly sprinkled with minute, brown 
dots set in small depressions. Similar 
punctate dots also are often found on the 
legs. The male genitalia consist of a pair 
of four-segmented forceps, with a rounded 
or conic penis cover located between the 
bases of the forceps. Each basal forceps seg- 
ment is short and wide, the second segment 
is narrow, tapering, and indistinctly sepa- 
rated from the third segment, the latter is 
long, slender, and bowed, while the fourth 
segment is short, being only about twice as 
long as wide. 
In Callibaetis subimagoes, the wings are 
dark gray, with the paths of the veins and 
crossveins white. 
The nymphs, fig. 226, are streamlined 
forms which swim with a rapid, darting 
motion. They live in still water, usually in 
permanent ponds. The nymphal maxillary 
palps have two and the labial palps have 
three segments. The tarsal claws are long 
and slender, and provided with a row of 
minute ventral denticles, figs. 264, 265. The 
abdominal gills are sheetlike and slightly 
undulated, with a dense net of pinnately 
branching tracheae. The first and second 
pairs of gills are always double, with the 
ventral member often bearing a secondary, 
recurved flap. The gills on segments 3-6 
are single, each having a_ well-developed, 
